1. Field of the Invention
The present invention relates to a flow meter, particularly for liquids, having an impeller which is arranged in a vertical line or measurement bore and can be driven by a flow stream, the impeller having a bearing shaft, the ends of which are rotatably mounted in an axially and radially guiding bearing, and one or more vanes of the impeller having their flow-on or attack surfaces inclined to the direction of the oncoming flow, and having a sensor which detects the rotary frequency of the impeller.
2. Description of the Prior Art
In such flow meters it is known to manufacture the impeller of a material whose density corresponds to that of the flowing fluid. In this way the result is obtained that the impeller floats in the flow fluid so that the friction of the mounting shaft in its bearings which must be overcome is kept as small as possible. This is necessary in order to keep measurement inaccuracies due to frictional losses as low as possible, particularly in the range of low velocities of flow.
The development of the impeller with a density equal to that of the flow medium, however, affords great difficulty since, on the one hand, the mounting shaft must consist of metal due to the high resistance to wear which is required while, on the other hand, the selection of the material for the vane part is very limited. This is of great disadvantage in particular when, for instance, a corrosive flow fluid permits the use of only very specific materials for the impeller, for instance metallic materials.